I have been doing some research on floors, and it looks like Bamboo is the way to go. Bamboo floors are comparable to hardwood floors, but instead of taking year 60 years to grow, bamboo can mature in 3 years. Bamboo is not really a "wood" at all, but a grass. However, the floors behave much like wood floors. The eco-friendliness definitely factors in our decision to go with bamboo, but we also like the look. Below are a couple of pics of beautiful bamboo floors.
Our original plan was to put a marble tile in the entrance, kitchen and corridor, but we have now decided to replace the existing wood floors in the living room and dining areas too. To achieve a coherent look we will use the same flooring material (bamboo!) in the whole first floor.
This is the actual floor that we have chosen for now (Woven Bamboo Toast):